Removal of pitch and resin is very important for pulping process. If not effectively removed pitch and resin may create fouling problems upon or after pulping and washing, cause increased consumption of bleaching agent(s) and/or form deposits later on the surfaces of papermaking equipment.
Deresination of birch wood in Kraft pulping is especially difficult because birch contains high amounts of unsaponifiable components, betulin being a major unsaponifiable component. Betulin is a naturally occurring pentacyclic triterpenyl alcohol found in birch wood and constitutes up to 35% of the birch bark. Betulin has a melting point at 256° C., which is significantly higher than those of many other pitch components. It is almost insoluble in water and chemically quite unreactive. It does not fully dissolve during the Kraft digestion process and can create deposition problems in the papermaking process.
One way to alleviate the problem is to remove the bark completely from birch before Kraft cooking. Debarking, however, leads to wood loss and yield reduction. As such, it is more desirable to use a digester additive to reduce betulin in the pulp upon Kraft cooking. This has the benefit of decreased betulin deposition and increased pulp yield relative to the current debarking process.
The birch deresination problem has been known for many years, and the only established method in pulping, primarily employed in Scandinavian mills, is the addition of tall oil or rosin soap to chips before the cook process. Black et al., Pitch Control, Wood Resin and Deresination, TAPPI Press, Chapter 8 (2000) and Dunlop-Jones et al., Journal of Wood Chemistry and Technology, 9 (3), 365-386 (1989) teaches that tall oil increases the amount of saponifiables, thereby boosting the ratio of saponifible-to-unsaponifiable wood resin, which in turn helps emulsify the unsaponifiables and drive them into black liquor.
Tall oil or tall oil soap has been used for many years for reduction of betulin in birch Kraft pulping. However, this method is moderately effective; only removing approximately 50% of betulin when tall oil is used at a 10-30 lb/ton of oven-dried (OD) pulp level. Addition of tall oil is practiced along with effective debarking which leads to a partial wood loss.
The effect of synthetic dispersants has also been investigated. For example, a dodecyl-benzene-sulfonic acid surfactant at 0.5% load has the same deresination effect on birchwood as 3% of softwood tall oil (E. L. Black and H. Allen “Pitch Control, Wood Resin and Deresination”, TAPPI press, chapter 8, 2000). However, cost restrictions had put limitations for commercial applications.
There are teachings regarding the isolation of betulin from the bark for medical and cosmetic formulations. This interest stems from the fact that betulin and its derivatives demonstrate strong antiviral, anticancer and anti-inflammatory properties and they have been studied extensively for their pharmaceutical applications. For examples see P. A. Krasutsky, “Birch Bark Research and Development”, Natural Product Reports, v. 23, 2006, pp. 919-942; R.U. Pat. No. 2291684; U.S. Pat. Nos. 6,890,533, 6,656,970 B2, 7,198,808, and 6,689,767; and U.S. Pat. Appl. 2003/0109727 A1.
It has been previously known that vegetable oils can be used for pitch and resin removal; e.g., see UK Pat. No. 1,466,502. However, these do not mention the effects on betulin and betulin type components.